This section provides background information related to the present disclosure which is not necessarily prior art.
The definition of the Next Generation Network (NGN) always changes with the development of the NGN. In the “2004 Global NGN Peak Forum” hold by the International Telecommunication Union (ITU), the standard of the NGN is defined as a packet based network, which can offer various services including telecommunication services and utilize transport technologies that support different bandwidths and Quality of Service (QoS) guarantee. The final direction and extent of the development of the NGN is thus determined.
In view of the current deployment of the NGN, two critical components, a Media Gateway Controller (MGC) and a Media Gateway (MG), are generally utilized for networking. The MGC is responsible for a call control function, and the MG is responsible for a service bearer function, thereby realizing separation of the call control plane and the service bearer plane. The above two components can evolve separately, so that it is possible to share network resources fully, simplify equipment upgrade and service expansion, and lower the cost of development and maintenance greatly.
The media gateway control protocol is the main protocol for communication between an MGC and an MG. At present, the widely-used protocols include the Gateway Control Protocol/H.248 (H.248/MeGaCo) and the Media Gateway Control Protocol (MGCP), and the communication protocol among MGs is the RealTime Transfer Protocol (RTP), as shown in FIG. 1.
The MGCP is established by the Internet Engineering Task Force (IETF) in October, 1999 and revised in January, 2003. Version 1 of the H.248/MeGaCo protocol is established jointly by the IETF and the ITU in November, 2000, and version 3 of the H.248/MeGaCo protocol is released by the ITU in September, 2005.
Eight basic commands, Add, Modify, Subtract, Move, AuditValue, AuditCapabilities, Notify and ServiceChange, are provided by the H.248/MeGaCo protocol between the MGC and the MG.
Nine basic commands, NotificationRequest (RQNT), Notify (NTFY), CreateConnection (CRCX), ModifyConnection (MDCX), DeleteConnection (DLCX), AuditEndpoint (AUEP), AuditConnection (AUCX), ReStartinProgress (RSIP) and EndpointConfiguraton (EPCF), are provided by the MGCP between the MGC and the MG.
The H.248/MeGaCo protocol is developed from the MGCP. Taking the H.248 for example, an MG bears services by means of the resources thereon. Those resources can be abstractly expressed as terminations, including physical terminations and temporary terminations. The physical termination is a physical entity of semi-permanent existence, such as a Time Division Multiplexing (TDM) channel. The temporary termination is a public resource that is temporarily obtained upon request and released after having been used, such as an RTP stream. The combination of terminations is abstractly expressed as a context. A context may include multiple terminations. The relationship among terminations is usually expressed as a topology. A termination that has not been associated with other terminations is included by a special context called Null context.
In such an abstract model of protocol, connection of a call lie actually in operations of terminations and contexts, and the operations are accomplished by command requests and replies between the MGC and the MG. Command parameters, also called descriptors, are classified into property, signal, event and statistic.
In particular, property represents the specification of resource requirements, usually sent to the MG by the MGC or set by the MG itself, such as a maximum or minimum value set for a jitter buffer; signal is used by the MGC to instruct the MG to operate the resources, such as play a dial tone, a ring back tone or a busy tone to a user; event is used by the MGC to instruct the MG to monitor status, such as monitor off-hook, hang-up, dialing and flash-hook performed by a user; and statistic represents the information of resource usage. These statistic parameters are usually calculated by the MG, and some of them can be enabled or disabled, i.e., activated or deactivated, selectively by the MGC. Certain parameters with a service correlation are aggregated logically into a package.
At present, a typical abstract logic model for an Internet Protocol (IP) voice call is that, two parties of the call, i.e., a calling party and a called party, each has a context containing two terminations, and the two parties of the call is present at different MGs. In particular, for an Access Media Gateway (AMG), an Integrated Access Device (IAD) or a Trunk Media Gateway (TMG), the two terminations may be a physical termination and a temporary termination respectively, i.e., connected to a circuit network and a packet network. For a Border Media Gateway (BMG) or a Packet Media Gateway (PMG), the two terminations may be two temporary terminations, i.e., connected to different packet networks. Each of the terminations described above represents a transmission type or media codec type, such as TDM, RTP, and Adaptive Multi-Rate (AMR). Therefore, system resources, such as a Digital Signal Processor (DSP), are also required for the codec conversion between any two terminations.
If the two parties of a call are present at the same MG, such a call may be treated as an internal connection, and no conversion between two codec formats may be required practically. For example, two subscribers for the Plain Old Telephone Service (POTS) at one AMG may make a call without a transfer of (POST1-IP1)-(IP2-POST2), and without a codec conversion, i.e., TDM-RTP, performed by a DSP. In other words, one context containing two physical terminations rather than two contexts each containing one physical termination and one temporary termination may be utilized. Additionally, two media streams at one PMG may also interwork without a transfer of (IP1-IP1)-(IP2′-IP2), and without a codec conversion, i.e., RTP1-RTP2, performed by a DSP. In other words, one context containing two temporary terminations rather than two contexts each containing two temporary terminations may be utilized. As a result of the reduction of the codec conversion, the expensive resources, such as a DSP, may be saved and the QoS of media transmissions may be further guaranteed.
In such a case in which an internal connection may be created, currently, there are two implementation modes for making determination and performing control. One is a controlled mode, in which the MGC determines two parties of a call are present at the same MG, and instructs the MG to add two terminations representing respectively the two parties into one context. The other is an autonomous mode, in which the MGC instructs the MG to create one context for each party of the call without determining whether the two parties of the call are present at the same MG, while the MG determines by itself the two contexts are present at the same MG, and connects the two terminations representing the two parties of the call directly.
In practice applications, the above two modes exist concurrently. However, because there is no standardized means for determining and controlling an internal connection, the MGC and the MG do not know how to deal with the scenarios that are needed to be supported. For example, the scenarios may be that, the MGC supports the determining and controlling of an internal connection, and the MG can also create an internal connection as instructed by the MGC; the MGC supports the determining and controlling of an internal connection, while the MG does not support the creating of an internal connection (for example, there is no internal logic for connecting two TDM channels); the MGC does not determine and control an internal connection, while the MG determines and controls an internal connection by itself; and the MG can determine and control an internal connection by itself, but the creating of an internal connection by the MG itself needs to be disabled when the MGC is implementing a service (such as a loop-back test). This becomes especially severe if the MGC and the MG are supplied from different equipment vendors.